<!DOCTYPE html>
<html>
  <body>
    <div style="position: absolute">
      <iframe src="data:text/html,<body contenteditable>foo</body>"></iframe>
    </div>
    <script type="text/javascript">
      onload = function() {
        var iframe = document.querySelector("iframe");
        var win = iframe.contentWindow;
        var body = win.document.body;
        iframe.focus();
        body.focus();
        var sel = win.getSelection();
        sel.collapse(body.firstChild, 0);
      };
    </script>
  </body>
</html>
